Current manufacturing techniques for application of coatings, for plating, or for deposition include gilding, mechanical plating, autocatalytic coating processes, such as alkaline electroless nickel boron coating, electroplating, such as chrome plating, copper plating, galvanization, such as hot-dip galvanization, tinning, and chemical and physical vapor deposition methods.
In gilding a thin film of a metal, such as gold, is coated onto a surface of a substrate such as wood, stone, or to give a thin coating of the metal. Mechanical plating is a process that applies a coating by cold welding fine metal particles to a surface of a substrate. In alkaline electroless nickel boron coating, the mixture of amorphous nickel boron is deposited from an aqueous solution which contains either an alkylamineborane or sodium borohydride as a reducing agent, a source of nickel ions, a buffer, a complexing agent, and optional control chemicals.
Electroplating is a process that uses electric current to reduce a metal cation dissolved in a solution to form a metal coating onto a cathode. Chrome plating involves electroplating a thin layer of chromium metal onto a metal or plastic surface of an object. The copper plating process involves complex systems, such as an alkaline-complexed bath, acid-complexed bath, and mildly alkaline-complexed bath. Galvanization, is a process of applying a protective zinc coating to steel or iron. Hot-dip galvanization is the process of coating an easily oxidizable metal, such as iron, steel or aluminum, with a coating of zinc by immersing the easily oxidizable metal in a bath of molten zinc.
Corrosion occurs in the presence of an electrolyte solution and involves oxidation (electron donating) and reduction (electron consuming) reactions that dissolve materials, particularly metals. In the acidic pH region, hydrogen ions (H+) and dissolved oxygen (O2) are the primary oxidizing agents, causing the dissolution of metals (M) according to:Cathodic Reactions: 2H++2e−→4 H2 (0 V vs. NHE)O2±4 H++4e−→2H2O (1.23 V vs NHE)Anodic Reaction: M→Mn++n e−
In most cases, the dissolved metal cations (Mn+) are transported away from the surface, form salts with anions in the electrolyte, and precipitate out of the solution. Muste, M. et al. “Two-phase flow insights into open-channel flows with suspended particles of different densities,” Environ. Fluid Mech. 9, 161-186 (2009). However, under certain conditions, re-deposition of the metal ions can occur.
Surface films set the surface potentials that govern the re-deposition process. In an aqueous solution, surface potentials may be controlled by surfactants, potential-control agents, such as hydrogen peroxide or vanadium oxide, or by external electric fields. In the case of lead (Pb) deposition in an acidic environment, Rhodamine B, has been employed to prevent dendrite growth during electro-deposition of Pb (see, Farmer, J. C., Muller, R. H., Effect of Rhodamine B on the Electrodeposition of Lead on Copper, J. Electrochem. Soc. 1985, 132, 313-319). As with most electrochemical processes, temperature plays an important role and directly affects reaction kinetics, fluid properties, phase changes, solubility.
Electroless plating uses a reduction agent in the process, typically formaldehydes, hydrazine, borohydrides, amine boranes, and derivatives. The ion to be deposited is added in various forms, for example, as a hydroxide or as a salt. Most processes involve replacement reactions where the element to be deposited is replaced in the precursor or within the reduction agent. This process does not rely on redox reactions or electrochemical potentials to deposit an element and thus is limited to use of specific materials.
Many of the methods of applying coatings onto a substrate surface exhibit limitations, such as cost, effectiveness, safety, etc. For example, copper is an active metal that is difficult to plate onto a passivated surface, making direct plating of iron based metals difficult. Another problem with some plating techniques is the high temperatures at which the plating occurs. Another possible disadvantage of some of the above-mentioned coating techniques are limitations due to electrical insulation of the substrate. A new method of coating the surface of a substrate is thus needed.
These and other objects, aspects, and advantages of the present disclosure will become better understood with reference to the accompanying description and claims.